The processing of fibrous material takes place in a refining gap which is formed between the refining elements on two opposed refining discs rotating relative to one another. The fibrous material is thus subjected to mechanical action by processing means on the refining elements, and at the same time the material moves outwardly by the action of centrifugal force. The processing means can be formed as continuous or discontinuous bars, teeth or in some other way.
During the defibering of fibrous material in the form of chips the chip bits are intended to be disintegrated to individual fibers with the least possible shortening of the fibers. Tests have shown that the design of the refining elements in the inner portion of the refining gap is of great importance for the feeding of the material through the refining gap as well as for the overall defibering process. During the disperging of recycled fiber pulp it is desired to obtain a processing which does not cause any shortening of the fibers or lowering of the freeness value (CS, F) of the pulp.
The processing which causes fibrillation and fiber shortening mostly takes place when the refining means are formed as bars by action of the edges of the bars.
Conventional refining elements with processing means in the form of bars with intermediate grooves can also give rise to a non-uniform material flow through the refining gap. This implies at the same time that the load on the motor or motors driving one or both of the refining discs will be uneven. As a result, the process is difficult to control, and the energy consumption increases. It also can affect the quality of the processed pulp.
It is also known to form the refining elements with processing means in the form of projecting pins, where the pins from one refining element extend into the intermediate space between the pins on the opposed refining element. This type of refining elements is shown, for example, in Swedish patent specification No. 510,948. With these refining elements a lenient defibering process is obtained, which does not cause any fiber shortening. There is risk, however, of an insufficient defibering effect.